It is necessary in many electrotechnical applications to limit the electric current which flows in an electric circuit to a maximum value. In particular so-called inrush peaks, which primarily occur when inductive consumers are switched on, must be typically limited to maximum values. This is particularly true in motor vehicle electrical systems in which, for example, the starter represents a very low-resistance load having high inductivity which, when switched on at the beginning of the starting process, results in a current peak and thus in a voltage dip in the electrical system. If the current peak can be limited, the voltage dip in the electrical system also turns out to be smaller. After the current peak has ended, i.e., when activating a starter in a vehicle after approximately one hundred milliseconds, the current limiting should no longer be effective if possible, so that the then-flowing current is not needlessly reduced.
For example, limiting of high current peaks may be implemented by using electronic power components. There are also suggestions in which an NTC resistor, i.e., a resistor having a negative temperature coefficient, is used for current limiting in the supply lead to the consumer, e.g., in the supply lead for the starter. Such an NTC resistor limits the current peak which occurs during the starting operation since the resistance of the cold component is relatively high. When the NTC resistor is heated by the electrical power, which is converted in the resistor when current flows, the value of the NTC resistance decreases and reduces the current through the consumer only slightly. DE 41 22 252 A1 describes such current limiting for a starter in a vehicle in which the negative temperature coefficient of the resistor is utilized for damping the current peak in the cold state and to conduct the current well in the heated state.
International Patent Application DE 2004/00 07 76 (not a prior publication) proposes to install in the starter line a resistor which is designed as a silicon resistor having slightly doped silicon. This resistor changes its resistance at higher temperatures by reaching the intrinsic conduction, thus resulting in a clear reduction of the resistance value. The use of such a resistor in the starter lead ensures that the starter current is limited when the resistor is cold, thereby damping the current peak which occurs when the starter is switched on, while the resistance value is reduced after heating of the resistor as a result of the current flowing through it and the flowing current is only slightly reduced.
Temperature-dependent resistors made of silicon having negative temperature coefficients (NTC resistors) have the disadvantage that, with the used dopings in the range of 1014 per cm2, resistance values distinctly lower than at room temperature can be noticed only at temperatures around 300° C. Reaching such temperatures periodically makes very high demands on the construction and connecting technology. With distinctly lower doping of the silicon, the area needed for representing a certain resistance value is very large and/or the layer thickness is very small.